Inspection of Friction Stir Welded Joint Using EMAT Generated Fundamental Shear Horizontal Guided Wave Mode (SH0)

Friction stir welding (FSW) is unique in terms of the mechanical properties and metallurgical structure of the joint. Like any other weld joints, FSW joints have some characteristic defects generated during the joining process. These defects lead to reduction in the overall quality of the weld, thereby weakening the joint over time. Thus, there is a need for an inspection technique to evaluate the weld quality in FSW joints. The fundamental SH0 mode offers a unique advantage because of its non-dispersive nature. SH waves are very difficult to generate through conventional ultrasonic generation methods, but electro-magnetic acoustic transducers (EMAT) have proven to be very efficient in this aspect. In this paper, we present an inspection technique involving shear horizontal (SH) ultrasonic waves that gives a qualitative view of FSW joint in aluminium plates. Studies were conducted on a 2.5 mm aluminium plate with a friction stir welded butt joint, with SH waves of wavelength 6.35 mm wavelength generated by EMAT probes. The configuration of the EMAT transducers was in such a way that the receiver measured the specular reflection from the weld line. The method was found to be useful in detecting defects in the weld-line. Results from EMAT inspection are compared with radiographic images.